A track structure of a conventional optical disc is described by way of example hereinafter with reference to FIGS. 3 and 4. There are alternately disposed a plurality of groove tracks 3 and land tracks 4 on a disc-like recording medium in the direction of a radius of the disc-like recording medium. The respective tracks are formed in such a shape as to be wobbled in the direction of the radius by a minute amount. Further, the respective tracks are divided into a plurality of arc-like sectors aligned along the direction of the radius, and a header 6 having address information for identification of recording areas is disposed at the leading edge of the respective arc-like sectors. The respective headers 6 are aligned with each other along the direction of the radius, that is, radially disposed.
FIG. 3 shows in detail the header at the respective lead edges of the tracks, that is, an address information portion where ID information for corresponding recording areas is recorded. In FIG. 3, the address information of the respective tracks is radially disposed at twp places, that is, a first position 21, and a second position 22, respectively, in such a manner as to be aligned along the direction of the radius. Portions of the respective groove tracks 3 at the front of, and at the back of the header, respectively, are connected with each other while portions of the respective land tracks 4 at the front of, and at the back of the header, respectively, are connected with each other. In the case of an example shown in the figure, respective pieces of the address information correspond to respective recording areas of the information tracks, on the right-hand side in the figure. Further, the address information corresponding to the groove information track 3 on the right-hand side in the figure is disposed at the first position 21, and the address information corresponding to the land information track 4 is disposed at the second position 22, both the address information being disposed in the form of pits 23. That is, the address information is disposed such that respective positions of the address information in the tracks adjacent to each other, along the direction of the information track, differ from each other, and respective positions of the address information in the tracks, apart from each other by two tracks, along the direction of the information track, coincide with each other. That is, as seen on the boundary line between the land track and the groove track, it is configured such that disposition positions of the ID information are divided into a first area and second area, and a first ID information area and second ID information area are alternately used for every other track.
The ID information in the header is provided in the form of microscopic indentations (pits), which are formed as asperities etc. on a substrate of a disc at the time of fabricating the disc, concurrently with grooves and so forth. For a recording film, use is made of a phase-change recording film (GeSbTe), and recording marks are formed in the shape of an amorphous area, respectively.
The conventional example described above is described in detail in, for example, JP-B No. 2856390, and so forth.
Meanwhile, another conventional example wherein address information is recorded with wobbles of grooves instead of recording in a header is described in, for example, JP-A No. 106549/1997.
With this example, frequency modulated wobbled grooves are used for recording address data. There are provided about 3360 pieces of wobbles per one revolution of a disc. For 1 bit of address data, 7 cycles of the wobbles are used. To express a bit “1”, 4 cycles of the wobbles are used in the first half of the 7 cycles while 3 cycles of the wobbles are used in the last half thereof. In other words, the wobbles are provided at high frequency in the first half, and at low frequency in the last half, a frequency ratio in this case being 4:3. To express a bit “0”, the order is reversed, and it is expressed by wobbles at low frequency, corresponding to 3 cycles in the first half, and wobbles at high frequency, corresponding to 4 cycles in the last half. An address code word is composed of 60 address bits. The number of address code words per one revolution of a track is 8. Out of the 60 bits of the address code word, 14 bits represent parity (CRC) for detection of an error, and the first 4 bits represent synchronization information for synchronizing with the address code word. 20 bits out of the balance represent track information (track number).
However, with the conventional example in JP-B No. 2856390, as previously described, the header has no groove, and cannot be used as a recording area, so that there has arisen a problem of deterioration in utilization efficiency (format efficiency) of recording tracks, rendering the same disadvantageous from the viewpoint of attaining a high capacity.
Further, with the conventional example described in JP-A No. 106549/1997, it has been impossible to dispose the address information except in the grooves. This is because the tracks adjacent to each other have different track numbers, respectively, so that about 10 bits out of the 60 bits including parity inevitably represent different data. Accordingly, even if an attempt is made to record information in a land between the grooves, since wobble information of the grooves, adjacent to the land, on both sides thereof, are differ from each other, wobble information cannot properly be reproduced. Further, because there occurs a portion of the land, where respective phases of wobbles of the grooves adjacent the land, on both sides thereof, are not aligned with each other, portions of the land, narrow in width and portions of the land, wide in width will result, thereby creating a cause for cross-talk from adjacent tracks at the time of recording or reproduction, so that this example cannot be applied land/groove recording. As a result, since recording can be made only in either lands or grooves, it is still difficult with this example as well to aim at higher capacity.